This is a revised application for an institutional training grant for pediatric physician-scientists that will be centered in the Department of Medicine, Children's Hospital Boston. It is intended to support the postdoctoral training of pediatricians who will continue on to careers in academic pediatrics. Five postdoctoral positions per year are requested, for each of five years. Trainees will each train for an average of two years. The training faculty consist of 30 senior academic and scientific leaders at Children's Hospital, including all 13 Division Chiefs. Trainees will be selected, using rigorous and well-defined criteria, from those in clinical and research subspecialty fellowship training programs within the 13 Divisions within the Department of Medicine. They will take advantage of a supportive environment anchored by a Fellowship Program Office and an Office of Faculty Development (which also assists all other postdoctoral fellows at Children's Hospital Boston). All trainees will take an established course in research methods hosted by the Clinical Research Program of Children's Hospital. Trainees will pursue one of two tracks. Those in the clinical research track will receive didactic instruction at the Harvard School of Public Health in clinical research methods, with the choice of receiving an M.P.H. Those involved in laboratory research will take courses in molecular biology and genetics as well as biostatistics. All trainees will receive instruction in ethical scientific conduct. The proposed mentors have a strong track record in training pediatrician-scientists alongside PhD, non-MD scientists: during the past decade, they have trained 432 MDs and 314 PhDs. Of the 432 MDs, over 186 are productive academic physician-scientists, 140 of whom are pediatricians. Of these, 13, 23, and 85 are at the academic level of professor, associate professor, and assistant professor, respectively. There are 29 Department Chairs or Division/Section Chiefs among them. These former trainees currently hold in aggregate 86 NIH grants and have themselves trained over 285 second-generation trainees (including 18 professors, 37 associate professors, and 62 assistant professors). This training grant offers the opportunity to bring an increasing number of pediatricians into rigorous clinical and bench training environments under the direction of proven mentors, so that they can contribute to the next generation of academic pediatrician scientists. [unreadable] [unreadable]